A general goal in turbine engine technology is to provide the ability to accurately measure temperature within the turbine in order to optimize engine performance and maximize engine life. Typically, temperature measurements are provided through the use of thermocouples. These devices have certain disadvantages including relatively high response times which can be lowered only at the expense of decreased longevity. These disadvantages have motivated attempts to develop practicable sensors based on optical pyrometry. However, problems of accuracy and of temperature-dependent drift in detector responses have severely limited the application of these sensors therefore turbine engines. For example, problems have been encountered in developing a calibration system that will enable such sensors to perform in accordance with expectations in the pertinent industries. More relevant to the present invention, however, are problems associated with the combustion products of turbine engines. Such engines produce carbon particles carried by combustion gases through the turbine. These particles contaminate the lens of the optical pyrometer and emit radiation, thus presenting sources of error in measurement. Accordingly, the sensors are typically provided with systems which supply air used to purge such particles from a channel through which turbine blades are imaged (See, e.g., U.S. Pat. Nos. 3,696,678 Mossey and 4,037,473 Compton et al.), the channel thus serving as both an imaging channel and an air plenum. However, while the need to incorporate a purging arrangement has been long recognized, prior approaches have indicated neither an awareness of the subtleties involved in providing an aerodynamically efficient purging arrangement, nor the desirability of minimizing entry of particulates into the imaging channel or plenum in the first instance. Also relevant to the present invention is the forementioned problem of temperature-dependent drift in detector responses. Prior teaching has been that detectors used in optical pyrometers are best positioned remotely from high-temperature areas of the engine in order to avoid or minimize this drift. Under such an arrangement, fiber-optic cables are typically employed to transfer radiation from the imaging probe to the detector. The use of engine fuel to cool the detectors has been suggested for arrangements in which the detectors are positioned in closer proximity to high-temperature areas. However, it has been discovered that substantial thermal stability can be achieved by cooling the detectors with air delivered from the compressor.
Accordingly, an objective of the present invention is to provide a turbine engine that comprises temperature measuring apparatus based on optical pyrometry, wherein the turbine shroud is adapted to minimize entry of particulates into a plenum along which a portion of the turbine is imaged.
Another objective of the invention is to provide a turbine engine that comprises a temperature measuring apparatus based on optical pyrometry, wherein the apparatus and the turbine shroud are adapted with respect to each other such that a sight aperture through which the apparatus images a portion of the turbine is minimized in cross-sectional area in order to minimize entry of particulates into said plenum.
A further objective of the invention is to provide a turbine engine that comprises a temperature measuring apparatus based on optical pyrometry, wherein the apparatus is designed to provide a highly efficient arrangement for maintaining a particulate-free imaging lens and for purging particulates from said plenum.
Another objective of the invention is to provide such engines wherein the detector of the pyrometer is kept sufficiently cool to avoid substantial drift in its response by supplying cooling air delivered from a compressor.
Advantages provided by the invention, in addition to such further objectives as are evidenced hereinafter, will be apparent from the following description which includes the appended claims and accompanying drawings.